1. Field of the Invention:
The present invention relates generally to an air-conditioner for automobiles, and more particularly to an automobile air-conditioner incorporating a cooled air bypass unit for controlling the temperature of an upper part of the vehicle passenger compartment in the vicinity of the head of an occupant.
2. Description of the Prior Art:
There is widely known a variety of cooled air bypass units used for controlling the temperature of an upper part of the vehicle passenger compartment in the vicinity of the head of an occupant of the motor vehicle. According to one such known cooled air bypass unit exemplified in Japanese Utility Model Laid-open Publication No. 60-151710, the opening of a cooled air bypass door is controlled according to the solar radiation detected by a solar radiation sensor so as to improve the comfortableness of air-conditioning in the vicinity of the head of the occupant.
Since the known cooled air bypass door is actuated to open and close depending on the presence of the radiation of the sun, the occupant feels a sudden change of air-conditioning condition each time the motor vehicle goes from the shade into the sun and vice versa. There is accordingly a strong desire for an apparatus capable of providing a gentle change of air-conditioning condition.
According to one attempt proposed by the present assignee to improve the air-conditioning feeling, there is provided a multistage bi-level mode operation to vary the ratio of the amount of air discharged from a vent outlet and the amount of air discharged from a heat outlet for the purpose of changing the air-conditioning feeling smoothly. Such attempt however is not satisfactory because the temperature of air blown off into the passenger compartment drops gradually when the opening of the vent outlet is changed stepwise from the maximum to the minimum side during the multistage bi-level mode operation while the opening of an air-mix door and the opening of a bypass door are kept constant. Such a temperature drop does never occur theoretically but experiments indicate that it may be caused due to the structure of an air-conditioner unit.
Owing to this temperature drop of the discharged air, the air-conditioning feeling is considerably deteriorated.